The disclosure relates to “active implantable medical devices” as defined by the Directive 90/385/EEC of 20 Jun. 1990 by the Council of the European Communities, specifically the “multisite” implants to collect electrical potentials and/or selectively deliver electrical pulses to one or more pacing sites of to a set of sites, particularly in cardiology and neuromodulation applications.
The recent development of such multi-site stimulation devices has led to increasing the number of electrodes, so as to allow the choice of one or more detection/stimulation sites optimizing the operation of the device.
The following disclosure will mainly refer to electrodes used for the application of stimulation pulses, but this feature is not limiting and the disclosure applies equally to the case of electrodes used for detection of electric potentials collected at specific sites, the same electrode possibly being used for both sensing and pacing.
In the particular case of the implantable cardiac devices for ventricular resynchronization or “CRT” (Cardiac Resynchronization Therapy), which are cited here as a non limiting example, a device with electrodes for stimulating one and the other ventricles is implanted in the patient. The stimulation of the right ventricle (and right atrium) is done by a conventional endocardial lead, but for the left ventricle, the access being more complex, the stimulation is generally carried out by a lead inserted into the coronary sinus and then pushed into a coronary vein on the epicardium so that the end of the is positioned in front of the left ventricle.
This procedure is, however, rather difficult, because the diameter of the coronary vessels is reduced with the progress of the lead, so it is not always easy to find the optimum position during implantation. The proximity of the phrenic nerve can also lead to inappropriate stimuli.
To overcome these difficulties, “multielectrode” leads have developed, provided for example with eight or more electrodes, and it is possible to choose, after implantation, the electrode which corresponds to the site on which the stimulation is the most effective. This selection of the electrode can be carried out automatically by a measure of endocardial acceleration peaks (PEA), by a measurement of bioimpedance, or from any other sensor able to provide information representative of the patient's hemodynamic status. It can also be operated manually by the practitioner by a suitable programmer controlling a generator.
These pacing leads must have a diameter as small as possible in order to extend the possibilities of implantation while being the least traumatic for the body.
Furthermore, increasing the number of electrodes creates issues of delicate connection at the connection with the stimulation pulse generator.
The difficulties encountered are similar in neuromodulation applications operating by multipoint stimulation of the central nervous system. Neuromodulation consists, for example, in implanting a microlead in the cerebral venous network in order to achieve very specific target areas of the brain in order to apply electrical stimulation pulses to treat certain conditions such as Parkinson's disease, epilepsy, etc. The purpose can also be to stimulate the peripheral nervous system, the electrodes then being placed at nerves or muscles.
With currently known techniques, increasing the number of electrodes to be connected has a strong impact on the size and cost of internal electronics of the housing, the connector of the housing and the lead, so it may be preferred to use a demultiplexer circuit which makes it possible to decode signals and voltages on a limited number of conductors (typically 2 or 4). It would however be beneficial to be able to increase the number of electrodes while generally reducing the volume of connection between the signal source and the lead, requiring only that these two or four conductors to power and control the demultiplexer.
This technique of multiplexing/demultiplexing is already implemented in cardiology and neuromodulation applications.
In some cases, the demultiplexing circuit is located in the distal portion of the device, near the electrodes, being incorporated in the lead body. EP 1938861 A1, EP 2465425 A1 and US 2011/301665 A1 describe such arrangements. But it is noted that in these known constructions, the transverse dimensions of the lead body in its distal part are larger due to the need to tightly integrate the demultiplexing electronic circuit.
Alternatively, to avoid this difficulty, an intermediate component of quite large dimensions is provided midway between the generator and the lead tip (see in particular EP 2727623 A1), which complicates the implantation and creates a new risk because of the need to implement an additional element.
Moreover, the evolution of the conductor structures and of the lead electrode technology is such that it now becomes possible to produce leads with very small dimensions for stimulating and sensing electrical events in the heart.
Such structures may use conductors of a diameter of 40 to 60 μm and thus may include a plurality of conductors insulated from each other, typically, up to 100 separate conductors in a diameter less than 0.5 mm. It is not known to associate such structures to multiplexers without immediately meeting the above problems, in particular in terms of size, complexity and cost.
WO 2012/087370 A1 (corresponding to U.S. Pat. No. 8,639,341 B2) discloses an arrangement wherein the demultiplexing circuit is accommodated in a region of the connector body, with a support and connection block interposed between the multiplexed conductors and the non-multiplexed conductors. This block includes, in its center, an elongate support receiving the demultiplexing integrated circuit, where the circuit is electrically connected to the two respective groups of conductors coming from either side of the support. If this arrangement allows incorporating the demultiplexing methods to the connector, it has the disadvantage of a large footprint that significantly increases the length of the connector.
The present invention aims to overcome these limitations of the prior art and to propose a connection solution between a demultiplexer circuit and a multielectrode lead that is reliable and protected while being compact and which can be housed in the vicinity the lead connector, not requiring increase in diameter of the latter, and simplify the structure of the connections of the associated housing.